Bisphenol-A, otherwise known as 2,2-bis(4-hydroxyphenyl)propane, is commercially prepared by reacting phenol and acetone in the presence of an acidic catalyst, such as hydrochloric acid, sulfuric acid, or a cation-exchange resin. In one commercial method, acetone is reacted with a stoichiometric excess of phenol in the presence of hydrochloric acid to produce bisphenol-A. The effluent from the reaction contains hydrochloric acid, unreacted phenol, bisphenol-A and the phenol-acetone condensation reaction by-products having color bodies therein. The reaction effluent is passed through a distillation/evaporation system to separate hydrochloric acid, unreacted phenol, lower boiling reaction by-products, crude bisphenol-A, and higher boiling reaction by-products having most of the color bodies therein. The thermal treatment employed in the distillation/evaporation system results in some decomposition/interaction of bisphenol-A and the phenol-acetone condensation reaction by-products, forming more color bodies. The hydrochloric acid, the unreacted phenol and the lower boiling reaction by-products are recycled to the reaction zone and the higher boiling reaction by-products having most of the color bodies therein are purged from the system. The crude bisphenol-A is dissolved in an organic solvent and the high purity bisphenol-A is crystallized from the solution. The crystals are centrifuged, washed with the organic solvent and dried to produce high purity bisphenol-A. The solvent liquor, obtained from the centrifuge, is distilled to produce the organic solvent for recycle and the residual liquor contains the by-products including isomers and color bodies present in the crude bisphenol-A. A part of the residual liquor is purged from the system to maintain the product bisphenol-A quality and to avoid build-up of undesirable by-products in the system, and the balance is recycled to the phenol-acetone condensation reactor. The by-products and the color bodies formed in the phenol-acetone condensation reaction and the distillation/evaporation system are generally defined in the prior art.
The bisphenol-A produced by the above method and separated from the reaction mixture has been effectively removed from the tarry residue by a number of procedures including distillation, crystallization, solvent extraction, spray drying, evaporation, and the like, and combinations thereof. However, it has been calculated that substantial amounts of phenol and re-usable bisphenol-A values can be derived from the tars and liquors derived from the process of making bisphenol-A, and there still remains the need to treat the tars and residues resulting from the initial reaction of the phenol and acetone to recover all possible useful products in order to enhance the value of the bisphenol-A process. Furthermore, it is desirable to remove color bodies and to convert the by-products including isomeric impurities remaining in the residual liquor obtained from crystallizing the crude bisphenol-A with an organic solvent after removal of the organic solvent by distillation. In order to increase the economy of the process of making bisphenol-A in the foregoing reaction and process, in order to reduce the amount of waste resulting from the process, and in order to produce from the waste streams a recycle stream substantially depleted of color bodies, it is desirable to improve the foregoing process of making bisphenol-A from acetone and phenol in the presence of an acid catalyst.
In U.S. Pat. No. 4,107,218, a bisphenol-A recycle stream from the cationic exchange-catalyzed bisphenol-A synthesis process, is decolorized with a cation exchange resin. All or part of the bisphenol-A process mother liquid in this patent is contacted with acidic cation exchange resin to remove color bodies. Phenol is reacted with acetone in a reaction mixture containing a cation exchange catalyst to produce a product mixture containing unconverted reactants, bisphenol-A and phenol-acetone condensation reaction by-products, and the product mixture is separated into bisphenol-A/phenol adduct crystals and a mother liquor stream. The mother liquor stream is recycled to the reaction mixture, and at least a portion of the mother liquor stream is contacted with an acidic cation exchange resin to reduce the content of color bodies contained in the mother liquor recycle stream. In the same patent, there are no tarry residue streams or liquor streams resulting from the distillation of liquors to be treated, only the bisphenol-A/phenol adduct and a mother liquor stream.